EP0558552B1

EP0558552B1 - A process to obtain high-purity bisphenol a

Info

Publication number: EP0558552B1
Application number: EP91920054A
Authority: EP
Inventors: Maciej Kiedik; Jósef KOLT; Jerzy Marszycki; Eugeniusz Zajac; Teodor Bek; Zbigniew Swiderski; Anna Rzodeczko; Jerzy Mroz; Janina Olkowska
Original assignee: INST CIEZKIEJ SYNTEZY ORGA; INSTYTUT CIEZKIEJ SYNTEZY ORGANICZNEJ "BLACHOWNIA"; ZAKLADY CHEM BLACHOWINA; ZAKLADY CHEMICZNE "BLACHOWNIA"
Current assignee: Instytut Ciezkiej Syntezy Organicznej Blachownia; Zaklady Chemiczne Blachownia
Priority date: 1990-11-24
Filing date: 1991-11-13
Publication date: 1997-06-18
Anticipated expiration: 2011-11-13
Also published as: PL287944A1; DE69126621T2; PL164289B1; FI932203A; WO1992009550A1; KR930702262A; TW221416B; US5198591A; FI932203A0; ATE154582T1; EP0558552A1; JPH06206840A; DE69126621D1

Abstract

The invention relates to a process for obtaining a high purity bisphenol from a post-reaction mixture resulting from the step of synthesis of phenol and acetone in the presence of a strong acid cation exhanger catalyst, by the way of crystallation and separation by distillation followed by recovery of bisphenol-A from the step of thermal catalytic decomposition of by product of the principal process technology in a multistage process.

Description

The present invention relates to a method for manufacturing high-purity 2,2'-di(4-hydroxy-phenyl)-propane, also called bisphenol A. The bisphenol A is used as a feedstock for producing resins, such as epoxy and polycarbonate resins, including the optical polycarbonate grade where especially high purity and good colouration are required.
Bisphenol A is obtained from a reaction of phenol and acetone in the presence of a strong-acid cation exchanger as catalyst. The post-reaction mixture contains, besides the bisphenol A, unreacted phenol, acetone and water, or catalyst and water, and by-products, mainly 2-(4-hydroxy phenol)-2'-(2-hydroxyphenyl)-propane, i.e. ortho-para isomer of bisphenol A, the so-called o,p-isomer, 2-2-4-trimethyl-4-(4-hydroxyphenyl)-chromane, i.e. the so-called Dianin compound, trisphenols, polyphenols and coloured substances. Depending on the methods selected for further Processing the post-reaction mixture, recovery and purification of bisphenol A, the final product may contain some amount of by-products which deteriorate its purity and colouration and unfavourably affect further processing.
A number of methods for removing the impurities are known in the art. The most commonly used method is to remove acetone and water, or catalyst, acetone, water and part of phenol from the post-reaction mixture followed by recovery, by crystallization, of bisphenol-A/phenol adduct which is then separated by distillation into raw bisphenol A and phenol. The mother liquor remaining after adduct recovery, which contains primarily phenol and some by-products and dissolved bisphenol A, can be recycled to the reaction system. In a multistage process, the bisphenol A is recovered by thermal catalytic decomposition of the by-products of the principal process technology.
The Polish Patent No 153 396 describes a process to manufacture bisphenol A where the feed is obtained by mixing the recycled phenolic liquor with part of the post-reaction mixture collected in the reaction system. The initial concentration of bisphenol A in this feed is 12-20% wt of bisphenol A, the content of bisphenol isomers in the total amount by-products is less than 25% of the by products and the phenol-to-acetone mole ratio is (5-30):1. The reaction is conducted at 60-95°C in the presence of a catalyst such as a mixture of macro- and microporous cation exchanger resin in the weight ratio of (0.05-0.5):1, respectively. This reaction results in a mixture containing bisphenol A at a high concentration, i.e. 21-35% wt, and 12-24% wt of by-products. As a result of recycling the phenol liquor to the reaction system, the quantity of the impurities is increased. In order to prevent cumulation of undesirable substances in the process, the impurities are removed by removing off part of or the entire liquor stream from the reaction system and processing it as required, to recover a suitable amount of bisphenol A.
EP-A-0332877 describes a method to remove impurities from bisphenol A consisting of the addition of water to the post-reaction mixture following removal of the catalyst therefrom, and vacuum evaporation of the water and part of the phenol from the mixture, resulting in bisphenol-A/phenol adduct crystallization. The separated water is then contacted, as a mixture with phenol, with a weak-basic ion-exchange resin prior to recycling to the crystallized adduct and then on for further treatment. The substantial disadvantage of the method is that only a small percentage of the impurities are removed from the post-reaction mixture.
The UK Patent No 1565667 describes a method to recover bisphenol A and remove coloured impurities from all or part of the recycled mother liquor stream by contacting it with an adsorber bed for example of cation-exchange resin. This permits some impurities present in the mother liquor to be removed before it is recycled to the reaction system. Obviously, the volume of mother liquor which can be purified using this method is limited; furthermore, the adsorber does not adsorb all the impurities to be removed and additional regeneration is required, i.e. washing, drying and removal of impurities from the washing liquid. Thus, a portion of the impurities is transferred to the reaction system with the liquor being recycled, the result of which is recycled bisphenol A lower in quality than that produced in the reaction of phenol with acetone.
Some other methods for removing impurities and recovering bisphenol A from all or part of the post-crystallization liquor arising from the step of bisphenol-A/phenol adduct separation or from process by-products produced in the process for obtaining bisphenol A from their catalytic decomposition while distilling off the product being formed and recycling the waste products to the reaction, are also known to those skilled in the art.
According to Polish Patents No 113641 and 103054, impurities are removed and bisphenol A is obtained with high efficiency by a method where phenol, in the presence of cation-exchanger resin catalyst, is reacted with intermediates, such as p-isopropenylphenol, o-isopropenylphenol and their dimers, obtained by thermal catalytic decomposition of bisphenol A process by-products and introduced to the reaction in phenolic solution, the said phenolic solution of synthesis by-products being dewatered post-crystallization liquor or fractions formed during distillation of the dewatered post-crystallization liquor. The reaction of phenol with the products of thermal catalytic decomposition of the bisphenol A process by-products is, according to the cited Patents, conducted in a separate reactor, under different conditions than those accompanying the phenolacetone reaction, preferably in the presence of 5-20% by weight of water.
The methods, as described above, do not show good efficiency; part of the undesirable impurities are transferred, with the adduct, into subsequent steps of bisphenol A process.
EP-A-0332203 describes a method to obtain high-purity bisphenol A, comprising a principal process and a so-called sub-process. In the principal process, phenol is made to react with acetone and the post-reaction mixture is treated to obtain a solution with a desirable concentration of bisphenol A: this is the so-called step I of concentration control and is followed by step I of bisphenol A/phenol adduct crystallization, step I of adduct separation from the mother liquor and step I of phenol removal from the adduct to obtain a high-purity bisphenol A. The sub-process consists of the following: step II of phenol reaction with p-isopropenylphenol, step II of bisphenol A concentration control, step II of bisphenol-A/phenol adduct crystallization, step II of adduct crystalline fraction II separation from mother liquor II, and step II of mother liquor II processing to obtain p-isopropenylphenol and phenol, the mother liquor I from the principal process being fed to the sub-process. The adduct crystalline fraction from the sub-process is fed to the principal process.
EP-A-0332203 also claims another variant of the process to obtain a high-purity bisphenol A. The principal process comprises the following: step I of reaction where phenol is made to react with acetone and catalyst is removed, a step of crystallization where bisphenol-A/phenol adduct is recovered, a step of crystalline adduct separation from mother liquor, and a step of phenol removal from crystalline adduct. The sub-process consists of the following: phenol reaction with p-isopropenylphenol in the presence of an acid catalyst and catalyst removal to obtain phenolic solution II, removal of phenol from phenolic solution II to obtain raw bisphenol A, separation of low- and high-boiling substances from raw bisphenol-A by distillation to obtain distilled bisphenol-A, and processing of the separated low- and high-boiling substances to obtain p-isopropenylphenol and phenol. The mother liquor from the principal process is fed to the sub-process and the distilled bisphenol-A from the sub-process is fed to the principal process.
The resulting bisphenol-A shows high purity due to "dilution" of impurities by introduction of adduct or bisphenol-A, recovered in the sub-process, to the principal process as a starting material. The main disadvantage of the process to obtain high-purity bisphenol-A according to EP-A-0 332 203 is the complexity created by the introduction of the sub-process comprising a number of steps of comparable complexity to the principal process. This results in a considerable increase in the investment and operating costs of the bisphenol-A plant where the process is used.
EP-A-0 210 366 is directed to a process for making bisphenol-A from phenol and acetone. Improvements in acetone conversion and bisphenol-A production are obtained by feeding acetone to a rearrangement reactor in which by-products are rearranged before they are recycled to the condensation reactor. This document does not specifically disclose any washing steps in which bisphenol-A/phenol adduct is washed with a phenolic solution. There is no disclosure of the processing of by-products in a thermal catalytic decomposition reactor located upstream from the catalytic rearrangement reactor. This document does not disclose dissolution and recrystallization of a bisphenol-A/phenol adduct. Furthermore, the bisphenol-A/phenol adduct of the preferred embodiment of EP-A-0 210 366 is formed after the removal of acetone, water and phenol in an evaporator.
In the process disclosed in EP-A-0 319 326, a mixture including bisphenol-A, phenol and impurities is combined with water, cooled and crystallized in a crystallization step, forming a crystalline bisphenol-A/phenol adduct in a slurry. The slurry is subjected to a separation process, separating the adduct from a filtrate. The adduct is washed with recycled phenol in a washing step. The washing liquid is recycled to the crystallization step. The purified adduct is separated into phenol and bisphenol-A/phenol product. The phenol is used in the washing step. There is no disclosure of recycling any washing liquid to the condensation reactor, or of recycling the filtrate. The process described in EP-A-0 319 326 does not include dissolution and recrystallization of the adduct. Furthermore, there is no disclosure of subjecting the process by-products to thermal catalytic decomposition followed by rearrangement.
The present invention is aimed at elaborating a process to obtain high-purity bisphenol-A from post-reaction mixtures containing high concentrations of by-products, wherein the faults and disadvantages present in the known process are not encountered.
According to the present invention the following reactions are conducted simultaneously in a reaction system wherein step I of the process comprises : reaction of phenol with acetone, reaction of phenol with p-isopropenylphenol resulting from thermal decomposition of process by-products recycled to the reaction system, and isometrizational rearrangement of process by-products to obtain bisphenol-A in the presence of a micro- and macroporous cation-exchange resin catalyst mixture. Step II of the process comprises cooling the post-reaction mixture together with water and acetone to obtain a precipitate of bisphenol-A/phenol in phenolic solution. Step III of the process comprises separation of the precipitate into crystalline bisphenol-A/phenol adduct and phenolic mother liquor I. The crystalline adduct is washed with the phenolic liquor and step IV follows, wherein the bisphenol-A/phenol adduct obtained in step II is dissolved in the phenolic solution and the resulting mixture is cooled to obtain a bisphenol-A/phenol precipitate in phenolic solution. Step V comprises separation of the precipitate obtained in step IV into the crystalline bisphenol-A/phenol adduct and mother liquor II to be returned to step III of the process. The bisphenol-A/phenol crystalline adduct is then washed with phenolic solution and step VI follows, wherein a high-purity bisphenol-A is recovered by removal of phenol from the bisphenol-A/phenol adduct obtained in step V. Step VII of the process consists in distillation of the phenolic mother liquor I obtained in step III, and removal of acetone, water and part of phenol therefrom. Dewatered phenol liquor is returned to step I of the process to the reaction zone and step VIII follows, consisting of thermal catalytic decomposition of part of the mother liquor I obtained in step(s) III and/or VII, resulting in a distillate containing phenol, isopropenylphenol and process by-products. Step IX consists of catalytic rearrangement of the reactive components of the distillate obtained in step VIII, while leaving the p-isopropenylphenol contained therein substantially intact and the rearranged distillate is recycled to step I of the process. In step I, the by-products are usually present in the reaction system in an amount of 10-30% by weight and bisphenol-A is usually present in the post reaction mixture in the amount of 15-35% by weight. The ratio of macroporous to microporous catalyst is usually in the range of 0.05 to 0.5 and preferably in the range 0.1 to 0.25.
The content of acetone and water in the post-reaction mixture while cooling it in step II is usually 2-6% by weight of acetone and 1-45% by weight of water. The crystalline bisphenol-A/phenol adduct is washed in step III with mother liquor II obtained in step V usually in an amount of 0.2-2.0 parts by weight of the liquor per 1 part by weight the crystalline adduct. The bisphenol-A/phenol adduct can be dissolved in step IV using the mother liquor II obtained in step V and/or phenolic solution obtained in step VII. The crystalline bisphenol-A/phenol adduct is washed in step V with fresh and regenerated phenol obtained in step VI usually in a ratio of 1-3 parts by weight of fresh phenol per 1 part by weight of regenerated phenol. Bisphenol-A can be separated from the bisphenol-A/phenol adduct by vacuum distillation of a substantial volume of phenol and removal of phenolic residue from bisphenol-A by steam stripping. The volume of phenol distilled off the mother liquor I in step VII is typically 0.1-0.3 parts weight per 1 part by weight of mother liquor I. Mother liquor obtained in step III of the process can be sent to thermal catalytic decomposition in step VIII in an amount of 0.05-0.2 parts by weight. The catalytic decomposition is usually conducted in the range of temperature 200-300°C and in the range of absolute pressure of 1,3-66,6 mbar (1-50 mm Hg) in the presence of catalysts selected from the group comprising : Na₂HPO₂, NaHC0₃, Na₂C0₃, NaOH. The rearrangement of some at the components of the distillate from step VIII toward bisphenol-A in step IX as a result of thermal catalytic decomposition of part of mother liquor I can be conducted in the presence of oxalic acid used in an amount of 0.5-0.5% by weight.
Substantially, the method of the present invention is advantageous in that the mother liquor I from step I of crystallization is sent to those steps of the process which are not directly connected with any further steps of bisphenol-A/phenol treatment ad bisphenol-A recovery, thus making their efficiency highly favourable. A majority of the impurities present in the process are removed with the stream of washing liquors and solutions I. This results in high purity and a high percentage of the large-grain size fraction in the bisphenol-A/phenol adduct recovered, with good efficiency, in recrystallization step which proceeds in a solution substantially free of impurities.
As is generally known, crystallization of a crystalline fraction from solutions containing more impurities results in the formation of finer grains, characterized by larger surface which is responsible for transferring the impurities. Thus, as a result of an increase in the amount of fine grain crystals, the colouration and the content of impurities are observed to grow.
Quite unexpectedly, crystallization of the bisphenol-A/phenol adduct from phenolic solutions containing water and acetone was found to improve the purity and size of the crystals. It was also observed that recrystallization of the bisphenol-A/phenol adduct has a substantial effect on the results of purification and that, even when washing the bisphenol-A/phenol adduct crystals repeatedly, the same result is not attained. Nevertheless, it is still purposeful to wash also the bisphenol-A/phenol adduct recovered in recrystallization step. The adduct is then rewashed, preferably using the phenol recovered in the subsequent step of phenol removal from the adduct. The phenol is comparable to commercial product, as far as its purity is concerned. The result of rewashing can be made more satisfactory if the volume of the phenol used for washing is increased, by addition of fresh phenol which is thereby introduced to the process as a starting material. Introduction of the fresh phenol, as starting material, in this stage of the process and its utilization, as described above, prior to sending it to step I of the synthesis reaction through appropriate circulating systems for post-crystallization streams and washing liquids has, additionally, a favourable effect on the efficiency of the step of bisphenol-A/phenol adduct purification. The bisphenol-A product obtained according to the present invention is characterized by higher purity than those obtained according to the conventional, industrially used methods.

Example 1:

A vertical drum reactor (D=2400 mm, H=10m) was filled with a mixture composed of 70% microporous Wofatit-KPS cation exchanger and 30% macroporous Wofatit-PK-110 cation exchanger up to 7m. The reaction mixture obtained by mixing the stream of dewatered post-crystallization liquor containing 8% by weight of bisphenol A and 15.5% by weight of process by-products with the reaction mixture collected from the bottom of the reactor was made to flow through the catalyst bed at 3400 kg/hr. The temperature of the mixture at the inlet to the reactor was 85°C and its composition was as follows: bisphenol A - 642.6 kg/hr, by-products - 622.2 kg/hr in-cluding o,p-isomers - 149.6 kg/hr, phenol - 1883.6 kg/hr, acetone - 231.2 kg/hr, water - 20.4 kg/hr. The composition of the product obtained was the following: bisphenol A - 816 kg/hr, by-products - 550.8 kg/hr including o,p-isomers - 163.2 kg/hr, acetone - 192.2 kg/hr, water - 40.8 kg/hr, phenol - 1800.2 kg/hr. The resulting solution at 85°C was cooled down to 40°C to obtain the crystalline bisphenol-A/phenol adduct. The crystals at 1720 kg/hr were subjected to centrifugation to separate them from the mother liquor I and washed with mother liquor II at 344 kg/hr. The colouration of the 50% crystalline adduct solution was 70 APHA. The washed adduct was solved in the phenolic solution obtained as a result of distillation of the phenolic mother liquor I. The resultant solution was recooled to 39°C to precipitate the bisphenol-A/phenol adduct crystals, the adduct was centrifuged and the mixture was rewashed using a mixture composed of 2000 kg fresh phenol and 1000 kg of regenerated phenol which produced 1376 kg/hr of bisphenol-A/phenol adduct. The colouration of the 50% crystalline adduct solution in ethanol was 5 APHA. The crystals were melted and sent to distillation column to distill a major part of phenol at 160°C and 13,3 mbar (10 mm Hg). The remaining phenol was removed by steam distillation to obtain 940 of kg bisphenol A. The bisphenol A product shows the following properties: crystallization point: 156.8°C, colouration of 50% solution: 4 APHA, o,p-isomer: trace amounts, codimer: trace amounts, trisphenol: 15 ppm, principal product: 99.96% by weight.

Example 2:

1000 kg of the mother liquor I obtained according to Example 1 and remaining after crystallization and withdrawal of the crystalline adduct in step III of the process was subjected to distillation to remove acetone, water and part of phenol which were found in the following percentages by weight: acetone - 0.86, water - 0.26, phenol - 75.68, bisphenol A - 8, by-products - 15.2. The stream was sent to the reaction unit described in Example 1 and mixed with part of the stream of the reaction mixture collected in the bottom of the reactor. The temperature at the inlet to the reactor was 85°C and the composition of the feed as expressed in weight percentage was as follows: bisphenol A - 20; by-products - 15.2, including o,p-isomers - 3.5; acetone - 5.8; phenol - 58.18, water - 0.82. The composition of the post-reaction mixture as expressed in weight percentage in an amount of 3000 kg, was as follows: bisphenol A - 35; acetone - 3.8; by-products - 15.8, including o,p-isomers - 3.7; water - 1.9; phenol - 43.5.
The resulting solution was cooled to 40°C to crystallize the bisphenol-A/phenol adduct. 778.38 kg of the crystalline adduct was centrifuged to separate it from the mother liquor I and washed with 1556.79 kg of the mother liquor II. The bisphenol-A/phenol adduct, in an amount of 778. 38 kg, was then dissolved by heating it in 1082.43 kg of the mother liquor II from Example 1. The resulting solution was recooled to 39°C to precipitate the crystalline bisphenol-A/phenol adduct which was then recentrifuged and washed with 720 kg of a mixture composed of fresh phenol and phenol recovered from the bisphenol-A/phenol adduct by distillation; the phenols were mixed in a ratio of 1.5:1. The product obtained was 522 kg bisphenol-A/phenol adduct.
The phenol was removed from the adduct as described in Example 1 as a result of which 336 kg of bisphenol A with the following parameters was obtained: crystallization point: 156.7°C, colouration of 50%-solution in ethanol: 20 APHA; o,p-isomer: trace amounts, codimer: trace amounts, trisphenol: 52 ppm, principal component: 99.92% by weight.

Example 3:

Acetone, water and part of the phenol were removed from 500g of the mother liquor I obtained in Example 1 as a result of which their percentages by weight was as follows: acetone - 0.91, water - 0.30, phenol - 73.67, bisphenol A - 9.92, by-products - 15.2.
The resulting dewatered liquor was subjected to thermal catalytic decomposition with simultaneous collection of the distillate, in the presence of 0.79g of sodium hypophosphite as catalyst at 280°C and at pressure lowered to 6,5 mbar (5 mm Hg). The resulting 395 g of distillate was then subjected to catalytic rearrangement with simultaneous redistillation in the presence of 1.185g of oxalic acid as catalyst at 220 °C and at pressure lowered to 13,3 mbar (10 mmHg) 315g of redistillate was obtained where the components were present in the following percentages by weight: phenol - 55.72, bispenol A - 3.24, p-isopropenyl-phenol - 27.98, by-products - 13.06.

Example 4:

650g of dewatered phenol liquor obtained according to Example 2 was mixed with 100g of the distillate resulting from the catalytic decomposition and rearrangement according to Example 3 and, after supplementing the mixture with acetone to obtain 6.3% by weight of its total content in the mixture, the reaction was conducted in the presence of 100g of Amberlyst-15 ion-exchange resin for 5 hrs at 75°C with intense stirring to provide contact of the entire ion-exchange resin with the reaction solution. The post-reaction mixture obtained was found to contain 34.3% by weight of bisphenol A and 17,97% by weight of by-products including 3.96% by weight of o,p-isomer and 4.11% by weight of codimer. The resulting solution was cooled to 40°C to crystallize the bisphenol-A/phenol adduct which was separated from the mother liquor by filtration in a centrifuge and washed with an equivalent amount of post-crystallization liquor II obtained according to Example II.
260g of crystalline bisphenol-A/phenol adduct was obtained and dissolved by heating in 360g of phenolic solution obtained, as described in Example 2, remaining after washing the crystalline adduct obtained in crystalization step II. The resulting solution was recooled to 39°C to obtain crystalline bisphenol-A/phenol adduct which was then washed with an equivalent amount of fresh phenol and phenol removed by distillation from the adduct obtained in Example II, mixed in the weight ratio of 1.5:1. As a result, 235g of bisphenol-A/phenol adduct was obtained and the phenol was removed from the adduct by the method of Example 1 which resulted in 152.3g of bisphenol A with the following quality: crystallization point: 156.8°C, colouration of 50% solution in ethanol: 10 APHA, o,p-isomer: trace amounts, codimer: trace amounts, trisphenol: 35 ppm, principal component: 99.94% by weight.
The method of the present invention is illustrated in Fig. 1 showing the process block diagram.
The method of the present invention consists in reacting simultaneously phenol with acetone, and p-isopropenylphenol resulting from thermal catalytic decomposition of process by-product and recycled to the reaction system, and an isomerizational rearrangement of process by-products to obtain bisphenol A in the presence of a micro- and macroporous catalyst mixture in reaction system 1. The post-reaction mixture is cooled to obtain a bisphenol-A/phenol slurry adduct in a phenolic solution in unit 2. The slurry is separated in unit 3 to obtain crystalline bisphenol-A/phenol adduct and phenolic mother liquor I. The crystalline adduct is washed in unit 3 using a phenolic solution, i.e. mother liquor II obtained in unit 5. The bisphenol-A/phenol adduct obtained in unit 3 is dissolved, in unit 4, in a phenolic solution, i.e. in mother liquor II obtained in unit 5 and/or phenolic solution, obtained in unit 7, which is a distillate of the mother liquor I formed in unit 3. Upon cooling the mixture to obtain crystalline bisphenol-A/phenol adduct in unit 5 the slurry is separated into crystalline bisphenol-A/phenol adduct and mother liquor II to be turned back to unit 3. The crystalline adduct is washed with the phenolic solution obtained by mixing fresh phenol with the regenerated phenol obtained in unit 6 in the ratio of 1 part by weight of the regenerated phenol per 1-3 parts by weight of the fresh phenol. The purified, molten bisphenol-A/phenol adduct is vacuum-distilled in unit 6 to obtain high-purity bisphenol A and recover a substantial part of phenol. The remaining phenol is recovered by steam stripping. The regenerated phenol is mixed with fresh phenol and used, in unit 5, to wash the bisphenol-A/phenol resulting from recrystallization (unit 5). The mother liquor I obtained in crystallization (unit 3) is distilled in unit 7 to remove acetone, water and part of phenol, whereas dewatered mother liquor I is sent to synthesis unit 1. Part of mother liquor I obtained in unit(s) 3 and/or 7 is sent to unit 8 where it is subjected to thermal catalytic decomposition in the temperature range 200-300°C and in the pressure range 1,3-66,6 mbar (1-50 mm Hg) in the presence of catalysts such as Na₂HPO₂, Na₂CO₃, NaOH. A distillate containing phenol, p-isopropenyl-phenol and process by-products is obtained. The reactive components of the distillate are subjected, in the presence of 0.05-0.5% by weight of oxalic acid, to catalytic rearrangement toward bisphenol A leaving the p-isopropenyl-phenol contained therein substantially intact, in unit 9. The distillate, rearranged in unit 9, is turned back to reaction unit 1.

Claims

A process to obtain high-purity bisphenol-A from a post-reaction mixture resulting from synthesis from phenol and acetone, in the presence of a strong-acid cation-exchange resin catalyst, by way of crystallization and separation by distillation followed by recovery of bisphenol-A from thermal catalytic decomposition of the by-product of the principal reaction in a multistage process wherein in step (1) the following reactions are conducted simultaneously : reaction of phenol with acetone, reaction of phenol with p-isopropenyl-phenol resulting from thermal catalytic decomposition of process by-products recycled to the reaction system, and an isomerizational rearrangement of process by-products to obtain bisphenol-A in the presence of a micro- and macroporous cation-exchange resin catalyst mixture; in step (2) the post-reaction mixture from step (1) is cooled together with acetone and water to obtain a bisphenol-A/phenol slurry adduct in a phenolic solution; in step (3) the bisphenol-A/phenol slurry adduct in a phenolic solution obtained in step (2) is separated to obtain crystalline bisphenol-A/phenol adduct and phenol liquor I; whereafter the crystalline adduct is washed with phenolic solution, and in step (4) the crystalline bisphenol-A/phenol adduct obtained in step (3) is dissolved in phenol solution and the mixture is cooled to obtain bisphenol-A/phenol adduct slurry in a phenolic solution; whereafter the slurry obtained in step (4) is separated in step (5) into crystalline bisphenol-A/phenol adduct and phenol liquor (II) to be returned to step (3) while washing the crystalline bisphenol-A/phenol adduct with phenol solution, whereas in step (6) the high-purity bisphenol-A is separated by removing phenol from the bisphenol-A/phenol adduct obtained in step (5), phenol liquor (I) obtained in step (3) is distilled in step (7) by removing water and acetone and part of phenol therefrom, whereas dewatered phenol liquor is sent back to step (1); in step (8) part of the phenol liquor obtained in step(s) (3) and/or (7) is decomposed by thermal catalytic decomposition to obtain a distillate containing p-isopropenylphenol and process by-products, and in step (9) reactive components of the distillate obtained in step (8) are rearranged catalytically leaving the p-isopropenylphenol contained therein substantially intact, and the rearranged distillate is returned to step (1) of the process.
A process as claimed in claim 1, wherein the content of by-products in step (1) of the process is 10-30% by weight.
A process as claimed in claim 1, wherein the bisphenol-A content in the post reaction mixture is in the range 15 to 35 weight percent and preferably in the range 20 to 30 weight percent.
A process as claimed in claim 1, wherein the ratio of macroporous to microporous catalyst is in the range 0.05 to 0.5 and preferably in the range 0.1 to 0.25.
A process as claimed in claim 1, wherein the content of acetone and water in the post-reaction mixture being cooled in step (2) is 2-6% by weight of acetone and 1-4% by weight of water.
A process as claimed in any one of claims 1, 2 or 5, wherein, to wash the crystalline bisphenol-A/phenol adduct in step (3), phenol liquor II obtained in step (5) is used in an amount of 0.2-2.0 parts by weight of the liquor per 1 part by weight of the adduct.
A process as claimed in any one of claims 1, 2 or 5, wherein phenol liquor II obtained in step (5) and/or phenolic solution obtained in step (7) is used to dissolve bisphenol-A in step (4).
A process as claimed in any one of claims 1, 2 or 5, wherein fresh phenol and regenerated phenol, obtained in step (6), are used in an amount of 1-3 parts by weight of fresh phenol per 1 part by weight of regenerated phenol, to wash the crystalline bisphenol-A/phenol adduct in step (5).
A process as claimed in any one of claims 1 to 5, wherein purified phenol/bisphenol-A adduct is decomposed and phenol is recovered in step (6) by distillation and steam stripping at vacuum conditions.
A process as claimed in any one of claims 1, 2 or 5, wherein 0.05-0.2 parts by weight of phenol liquor I obtained in step (3) is subjected to thermal catalytic decomposition in step (8), the said thermal catalytic decomposition being conducted in the range of temperature 200-300°C and in the range of absolute pressure 1,3-66,6 mbar (1-50mm Hg) in the presence of alkaline catalysts selected from the group comprising Na₂HPO₂, NaHCO₃, Na₂CO₃, NaOH.
A process as claimed in claim 10, wherein rearrangement of some components of the distillate obtained in step (8) is effected in step (9) by thermal catalytic decomposition of part of phenol liquor I towards bisphenol-A in the presence of 0.05-0.5% by weight of oxalic acid.